Phase Equilibria, Crystal Structure and Hydriding/Dehydriding Mechanism of Nd4Mg80Ni8 Compound.
Phase Equilibria, Crystal Structure and Hydriding/Dehydriding Mechanism of Nd4Mg80Ni8 Compound.
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DOI：
10.1038/srep15385
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发表时间：
2015-10-16
影响因子：
4.6
通讯作者：
Li Q
中科院分区：
文献类型：
--
作者：
Luo Q;Gu QF;Zhang JY;Chen SL;Chou KC;Li Q
为了找出新型Nd-Mg-Ni储氢合金的最佳成分，通过检查平衡合金，建立了Nd-Mg-Ni系400°C的等温段。在富镁角发现了一种新的三元化合物Nd4Mg80Ni8。它具有I41/amd空间群的晶体结构，晶格参数为a = b = 11.2743(1) Å和c = 15.9170(2) Å，通过同步加速器粉末X射线衍射(SR-PXRD)对其进行了表征。高分辨率透射电子显微镜 (HR-TEM) 用于研究 Nd4Mg80Ni8 的微观结构及其氢致微观结构演化。加氢导致Nd4Mg80Ni8分解成NdH2.61-MgH2-Mg2NiH0.3纳米复合材料，其中高密度相界提供了大量氢原子扩散通道和氢化物成核位点，大大增强了氢化/脱氢（H/D）性能。 Nd4Mg80Ni8表现出良好的循环能力。采用真实物理图（RPP）模型研究了H/D反应的动力学机制。速率控制步骤是在100～350℃温度范围内进行氢化反应的扩散和在291～347℃范围内进行脱氢反应的表面渗透。原位 SR-PXRD 结果揭示了 Mg 到 MgH2 和 Mg2Ni 到 Mg2NiH4 的相变是氢压和氢化时间的函数。
In order to find out the optimal composition of novel Nd-Mg-Ni alloys for hydrogen storage, the isothermal section of Nd-Mg-Ni system at 400 °C is established by examining the equilibrated alloys. A new ternary compound Nd4Mg80Ni8 is discovered in the Mg-rich corner. It has the crystal structure of space group I41/amd with lattice parameters of a = b = 11.2743(1) Å and c = 15.9170(2) Å, characterized by the synchrotron powder X-ray diffraction (SR-PXRD). High-resolution transmission electron microscopy (HR-TEM) is used to investigate the microstructure of Nd4Mg80Ni8 and its hydrogen-induced microstructure evolution. The hydrogenation leads to Nd4Mg80Ni8 decomposing into NdH2.61-MgH2-Mg2NiH0.3 nanocomposites, where the high density phase boundaries provide a great deal of hydrogen atoms diffusion channels and nucleation sites of hydrides, which greatly enhances the hydriding/dehydriding (H/D) properties. The Nd4Mg80Ni8 exhibits a good cycle ability. The kinetic mechanisms of H/D reactions are studied by Real Physical Picture (RPP) model. The rate controlling steps are diffusion for hydriding reaction in the temperature range of 100 ~ 350 °C and surface penetration for dehydriding reaction at 291 ~ 347 °C. In-situ SR-PXRD results reveal the phase transformations of Mg to MgH2 and Mg2Ni to Mg2NiH4 as functions of hydrogen pressure and hydriding time.